The present invention pertains to methods of avoiding the discarding of data packets in congested data networks.
In present day communications systems, data is generally sent to remote sites or destinations by various paths or links. Some sites or destinations have a single access path or link to the network while other sites have multiple paths or links to the network. For example, in a satellite data network a communication path in the network originates at a ground station and data is sent through a plurality of space vehicles to a final space vehicle that sends the data to a destination ground station. The problem is that each space vehicle or other data reception equipment or channel has a limited capacity to handle data.
It is the nature of network traffic to be unpredictable with traffic volume flowing in peaks and valleys. To completely cover these peaks requires expensive hardware with capability that is under utilized the majority of the time. To satisfy customer requirements, the peaks of data must be handled or there is a high probability that the data may be dropped.
Assuming that the duration of the majority of these peaks are less than 40 ms or 50 ms, queuing or buffering the traffic during those peaks enables the traffic peak to be redistributed to a less loaded time, usually still meeting the time-out requirements. Generally, there is a predetermined time in which a data packet (data packets can include voice, video, email, etc.) must reach its destination or it simply expires. This time is generally much longer than the time required to reach the destination but it ensures that data packets which are lost or mis-sent eventually expire, rather than continuing to conjest and eventually jam the network. Increasing the size of memory buffers to handle data peaks is often the terrestrial solution. The problem with increasing the buffer size in space vehicles is the large investment in expensive radiation hardened hardware, which in turn increases the power and ultimately the weight and launch costs.
Packet switched communications networks, implementing multiple classes of service, typically control short-term congestion by discarding lower priority data packets when network buffers become full. Since space vehicles have limited data storage, data packets typically contain priority fields that are used by the space vehicle in network congested situations, to discard lower priority data packets to help alleviate the congestion. This leads to poor network throughput, since the originating ground terminal must resend the discarded packet after a time-out period. This can be a problem on terrestrial networks as well. The discarded data packet may be only one link away from its destination after traversing through numerous network nodes and using valuable resources along the network path. Thus, network performance suffers from these retransmissions.